Directly engaged syringe driver system

ABSTRACT

A syringe driver system comprises a rotatable threaded lead screw shaft and a plunger which directly engages the threaded shaft such that rotation of the shaft drives the plunger into the syringe body. The plunger is formed with a threaded shaft engaging portion in the form of a half nut to engage with and follow the threaded shaft. The syringe driver system further comprises a guide system to secure the plunger in direct engagement with the threaded shaft and to prevent rotation of the plunger. An arm of the plunger stem carries markers useful in determining the near end of infusion. The syringe body carries a marker or markers useful in determining a characteristic about the syringe, such as its volume.

BACKGROUND OF THE INVENTION

The invention relates generally to drug infusion systems and, moreparticularly, to a syringe driver for expelling fluid from a syringe anda syringe for use in the syringe driver.

Syringe drivers are used in the medical environment to infuse a givendose of a medicament into a patient from a syringe engaged with thedriver. The medicament is generally infused at a regular rate over aperiod of time which may vary from, for example, an hour to a number ofdays. Referring to FIG. 1, a conventional ambulatory syringe driver 10comprises a housing 12 which includes a rotatable threaded shaft or leadscrew 14 driven by a motor located within the housing. The motor ispowered by batteries also located in the housing. The threaded shaft 14is exposed and a driver block 16 with a threaded bore is mounted on thethreaded shaft such that rotation of the shaft drives the driver blockalong the shaft. The driver block is provided with a de-clutch button 18which, when depressed, de-clutches the driver block from the threadedshaft to allow free movement of the driver block along the shaft. Thedriver block has a clip or slot 20 by which a plunger 22 of a syringe 24can be secured to the driver block for controlled movement of theplunger 22.

While FIG. 1 represents a typical current ambulatory syringe driversystem, some non-ambulatory systems have differences. In suchnon-ambulatory syringe driver systems, the lead screw and driver blockare enclosed within the casework of the device, usually running parallelto, but spaced apart from the syringe barrel. An arm or slide extendssideways from the driver block out through the casework, to engage thesyringe plunger. The arm terminates with a plunger holder, which usuallyincorporates a mechanism for remotely de-clutching the half nut withinthe driver block.

Thus, a driving force can be applied to the syringe without exposing thelead screw. Additionally, many such non-ambulatory systems are poweredby both main power (wall power) and battery power.

In the operation of the syringe driver shown in FIG. 1, a syringe havinga cylindrical syringe body and a plunger slidably mounted in the body isclamped 26 to the housing by its body. The free end of the plungerextends from the syringe body and lies parallel with, but spaced apartfrom, the threaded shaft. The de-clutch button 18 is depressed to allowfree movement of the driver block along the threaded shaft such that theslot in the driver block is aligned with and receives the free end ofthe plunger. Once the free end of the plunger has been secured to thedriver block, the de-clutch button is released and the driver block onceagain engages the threaded shaft. When the motor of the driver isactuated, the driver block is driven towards the syringe body therebydriving the plunger into the syringe body causing fluid in the syringebody to be expelled and infused into the patient.

A disadvantage of such a syringe driver, as described above and shown inFIG. 1, is that the overall size of the syringe driver with respect tothe syringe is large. This is due at least in part to the driver blockthat is mounted on the threaded shaft. In particular, the driver block16 accounts for a significant portion of the overall size of the syringedriver 10 in that it spaces the syringe plunger 22 away from thethreaded shaft 14 and requires an additional length to the threadedshaft to accommodate the driver block when the largest syringe specifiedfor the driver 10 is used and the driver block must be moved to the farend of its travel to receive the plunger of that syringe. This isnecessary because of the internal components of the driver block, suchas the de-clutch button 18, the internal threaded portion, and the slot20 of the driver block. The threaded portion must be long enough tofirmly engage the threaded shaft and must have means to hold the threadsin contact with the threaded shaft even under heavy loads provided bythe syringe or downstream infusion system. However, certainapplications, such as ambulatory uses, would benefit from a smaller sizesyringe driver system.

Another disadvantage associated with conventional syringe drivers isthat there is a certain amount of play between the driver block 16 andthe threaded shaft 14 which gives rise to hysteresis in the movement ofthe block with respect to the threaded shaft as well as some backlash.It should be noted that the driver block, as well as the housing, motor,threaded shaft, and syringe clamp are all reusable elements. Because thedriver block is a reusable element, such hysteresis and backlash tend toworsen over time because of wear on the driver block. It would also beof value to lessen the possibility of wear of the driver block.

Additionally, driver blocks, depending on their complexity, canthemselves add a significant expense to the syringe driver system.Further, should replacement due to wear be required, the labor needed todisassemble the syringe driver housing, as well as the “down time” ofthe syringe driver system to replace the driver block are undesirablecosts for a hospital or other health care institution. Thus, animprovement over existing driver block designs would be desirable, aswell as making syringe driver systems smaller to make them more usefulin an ambulatory application.

Many ambulatory syringe drivers presently available are calibrated inmillimeters per hour; i.e., a distance rate, as they lack the complexityto determine the size of syringe fitted. Most medical infusionprescriptions are written in volume to be infused; i.e., milliliters perhour. Having to convert milliliters per hour to millimeters per hour canimpose an additional undesired step on medical care providers. However,most non-ambulatory syringe drivers are calibrated in milliliters perhour as they tend to be fitted with systems that can identify thesyringe type by its external diameter. It would be of benefit to providean ambulatory syringe driver system that can automatically recognize thesyringe installed and can therefore accept a flow instruction in volumeper time format, such as milliliters per hour to make setting the rateof infusion easier.

Additionally, it is also convenient for a pump or driver to present thecare provider with a warning that the syringe is nearly exhausted. Thishas been found to be beneficial when the preparation of a patient'smedicants takes some time but cannot be prepared too far ahead of time.With a near-end-of-infusion warning, preparation of those medicants canbegin. As mentioned above, ambulatory syringe drivers typically lackcomplexity and in most cases, do not include a mechanism to determinethe near end of infusion point. They usually only provide an alarm atthe end of infusion when the syringe is exhausted. Some non-ambulatorydevices however have mechanisms to determine not only the existence oflinear movement of the syringe plunger but also the near-end-of-infusionpoint and these features would be desirable in ambulatory designs aswell.

Hence, those skilled in the art have recognized a need for a syringedriver system having a reduced size as well as one with fewer movingparts subject to wear and replacement. Additionally, an ambulatorysyringe driver system light and small enough to be carried by a personand capable of receiving infusion instructions in volume per unit timeas well as one that detects linear movement of the syringe plunger andprovides a near end of infusion warning have been recognized as needed.It has also been recognized by those skilled in the art that it would beof value to have a syringe driver system that is lower in cost andeasier to manufacture. The present invention satisfies these needs aswell as others.

SUMMARY OF THE INVENTION

Briefly, and in general terms, in one aspect the invention is directedto a syringe driver system having a plunger and a threaded shaft fordriving fluid from a syringe body mounted on the syringe driver in amanner that provides a greater degree of infusion accuracy.

In another aspect, a rotatable threaded shaft is directly engaged by aplunger such that rotation of the shaft drives the plunger into thesyringe body and expels the syringe contents. In detailed aspects, theplunger is formed with a shaft engaging portion to engage with andfollow the threaded shaft. The shaft engaging portion comprises athreaded portion molded into the plunger, and the shaft engaging portioncomprises at least one recessed half-nut. In another detailed aspect theplunger comprises a flange having at least one disk, the shaft engagingportion is part of the flange, and the edges of the flange adjacent theshaft engaging portion are formed to guide the shaft engaging portiononto the threaded shaft.

In further detailed aspects the syringe driver system further comprisesa guide system to secure the plunger in direct engagement with thethreaded shaft and to prevent rotation of the plunger. In yet anotherdetailed aspect, the guide system comprises a first guiding elementrunning substantially parallel to the threaded shaft and a secondguiding element carried by the plunger at a position substantiallyopposite the position at which the plunger engages the threaded shaftsuch that the first and second guiding elements engage.

In another aspect, the system for infusing fluid comprises a cover and abase for accommodating the threaded shaft, syringe, and motor. In adetailed aspect, the apparatus further comprises a control system formonitoring operating parameters of the apparatus and controlling therotation of the motor and a detection system for detecting movement ofthe plunger. In another detailed aspect, the syringe includes one ormore identification markings indicative of a characteristic of thesyringe, such as its volume, the detection system includes a detectorfor detecting the identification markings and the detector systemprovides a signal to the control system in accordance with theidentification markings detected. In a further detailed aspect, the stemof the plunger has an elongate arm provided with a plurality of markingsto define a linear grid to indicate the movement and position of theplunger within the syringe body, the detection system includes aplurality of detectors for detecting the markings and the detectorsystem provides signals to the control system in accordance with themarkings detected.

In yet another detailed aspect, the detection system includes a lightsource, the detection system positioned adjacent the markings of theplunger stem arm such that the light source is on one side of the armand the plurality of detectors is on the opposite side of the arm andwherein the markings on the arm at a near end of infusion (NEOI) pointof the syringe have a first size and the markings elsewhere on the armhave a second size different than the first size such that the markingsat the NEOI point allow illumination of a first number of the detectorsand the markings elsewhere allow illumination of a second number ofdetectors different than the first number of detectors.

In yet a further aspect, a plunger for engaging a threaded shaft and forexpelling fluid from a syringe body comprises a stem, a stopperpositioned at an end of the stem, the stopper sized to fit within thesyringe body and a flange positioned at the end of the stem opposite thestopper, the flange having a threaded portion sized to engage thethreaded shaft.

In yet another aspect, a syringe for use in a fluid delivery apparatushaving a threaded shaft comprises a syringe body, a stem, a stopperpositioned at an end of the stem, the stopper sized to fit within thesyringe body, and a flange positioned at the end of the stem oppositethe stopper and outside of the syringe body, the flange having athreaded portion sized to engage the threaded shaft.

These and other aspects and advantages of the invention will becomeapparent from the following detailed description and the accompanyingdrawings, which illustrate by way of example the features of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a conventional, prior art ambulatorysyringe driver system with a mounted syringe showing a drive blockconnected between the lead screw of the syringe driver and the syringeplunger for translating the rotational motion of the lead screw tolinear motion of the plunger for expelling the contents of the syringe;

FIG. 2 is a side view of a syringe in accordance with aspects of theinvention shown in partial cross section and connected to an infusionadministration set, the syringe engaged with a part of a syringe driverembodying further aspects, other parts of the syringe driver not beingshown;

FIG. 3 is an end view of the syringe shown in FIG. 2 showing a guiderail slot in the plunger, the half nut, and identification markers inthe body flange;

FIG. 4 is a partial cross-section of the syringe shown in FIG. 2 moreclearly showing that there exists no bottom arm of the syringe plungerstem so that the plunger and lead screw of the syringe driver may bepositioned more closely together;

FIG. 5 is a cross-section view of an alternate embodiment of a syringeplunger showing an H-section configuration of the stem and the positionof the lead screw in the stem;

FIG. 6 is a partial cross-section top view of the syringe shown in FIG.5 showing the markers on the syringe plunger stem usable in indicatingnear end of infusion and end of infusion, and showing double plungerflanges with guide rail slots formed in both plunger flanges;

FIG. 7 is a perspective view of a half nut formed in the plunger flangesof the syringe shown in FIGS. 2 through 4 and which may also be formedin the syringe of FIGS. 5 and 6;

FIG. 8 is an example of an ambulatory syringe driver system usable withthe syringes shown in previous figures, and indicating the placement ofthe syringe of FIGS. 2 through 4 to be inserted in the syringe driver,the casing for the syringe driver being in an open condition;

FIGS. 9 and 10 demonstrate a mounting arrangement of a syringe inaccordance with aspects of the invention where the guide devicecomprises an arm that engages the slots of the syringe plunger flanges.In particular, FIG. 9 shows a syringe partially inserted into a syringedriver and engaged with the lead screw, the casing of the driver beingin an open condition, and FIG. 10 shows the syringe fully inserted andready for use;

FIGS. 11 and 12 show an alternate arrangement for mounting a syringe inaccordance with aspects of the invention wherein the lead screw islocated at the bottom of the casing and the guide rail is at the top.FIG. 11 shows the syringe driver casing in an open position while FIG.12 shows the casing in a closed condition with the syringe secured inposition for the infusion of its contents to a patient by operation ofthe syringe driver; and

FIG. 13 presents a block diagram of a layout of a syringe drive systemin accordance with aspects of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Turning now to the drawings, in which like reference numerals are usedto designate like or corresponding elements among the several figures,in FIG. 2 in a generally schematic view there is shown a syringe 30 foruse with a syringe driver 66 embodying aspects of the present inventionand together forming a syringe driver system 64. The syringe 30 includesa syringe body 32 having a side wall 34 which in two embodiments may becylindrical or elliptical in shape, formed with a nozzle end 36 at itsdistal tip and an open end 38 at its proximal end terminating in anoutwardly directed body flange 40. At the nozzle end 36, a fluidadministration set 37 may be mounted. Such sets are well known to thoseskilled in the art and include tubing, and in some cases, valves,injector ports, and clamps. Other devices may also be included in theadministration set.

In one embodiment, as shown in FIG. 3, the syringe body flange 40 issubstantially rectangular and the syringe body 32 is positioned to oneside of the syringe body flange 40 so that one side of the flange 40projects farther from the syringe body 32 than at the other side. Inother embodiments the shape of the syringe body flange 40 may deviatefrom the substantially rectangular shape shown in FIG. 3.

FIG. 4 presents a view of the syringe 30 without the driver 66 ofFIG. 1. A plunger 42, as shown in FIGS. 2, 4, and 8 is slidably insertedin the syringe body 32 and has a rubber- or latex-free stopper 44 fittedat one end within the syringe body and a plunger flange 46 at its freeend. The plunger flange 46 in this embodiment comprises two co-axial andparallel spaced-apart disks 46A and 46B. In contrast to conventionalsyringe plungers which have a cruciform stem, the stem 47 of the plunger42 shown in FIGS. 2, 4, and 8 only has three stem arms, the lowermoststem arm being omitted so that the lead screw 54 can be accommodated asshown in FIG. 2.

An alternate embodiment of a plunger is shown in FIGS. 5 and 6 whereinan “H” section plunger stem 57 is used. It has been found that thisconfiguration provides greater and more even rigidity of the plunger 42.In this embodiment, the syringe body flange 40 includes an opening (notshown) through which the stopper 44 is inserted during assembly of thesyringe 30. The opening is marginally smaller than the internal diameterof the syringe barrel and has slots in it corresponding to the stemedges. A disc 43 located just behind the rubber stopper 44 would be justsmall enough to fit through the hole with the stem edges engaging withthe slots. Due to its compliance, the rubber stopper 44 ahead of thedisc would compress to fit through the hole in flange 40, then expand toform a seal with the internal wall of the barrel of the syringe. As thedisc 46 does not enter the syringe barrel, its size is independent ofthe syringe barrel diameter. The slots in the syringe body flange 40engage the edges of the plunger stem so that the plunger 42 is unable torotate in relation to the syringe body 32 resulting in greater stabilityof the syringe and avoiding possible misalignment with markers formed inthe plunger, as is discussed below.

The plunger flange 46 has two special features. Referring now inparticular to FIGS. 3 and 7, first, two aligned and substantiallyU-shaped cut-outs 48 are provided in the disks 46A, 46B and each disk46A, 46B is formed with at least one thread. The embodiment shown inFIGS. 3 and 7 is provided with a half-thread 50 on each disk 46A, 46B.The threaded cut-outs 48 define a threaded portion 50 of the plungerflange 46. The threaded portion 50 effectively comprises a recessedhalf-nut. In alternate embodiments, threads may also be formed betweenthe disks 46A, 46B such as by making the plunger flange 46 a solid piecewithout separate disks 46A and 46B. The threads 50 may extend from oneend of the flange to the other. The edges of the plunger flange 46adjacent the threaded portion 50 are formed to guide the threadedportion 50 onto the threaded shaft of the lead screw 54. In thisembodiment, they are flared outward from a U-shape to form more of arounded V-shape. This shape facilitates inserting the syringe onto thethreaded shaft making syringe loading faster, easier, and more accurate.

The second feature of the plunger flange 46 is a guide slot 52 formed inthe circumferential edges of the disks 46A, 46B at a position oppositethe threaded portion 50. Since the plunger flange 46 is circular, theguide slot 52 is diametrically opposite the threaded portion 50. Theguide slot is located and shaped to accept a guide rail that keeps theplunger flange against the threaded lead screw shaft. Since thelowermost piece of stem has been omitted from the plunger 42 in oneembodiment, and in another embodiment, comprises two parallel stem armsthat are spaced apart, the area extending from the threaded portion 50of the plunger flange 46 to the stopper 44 is clear. This permitsplacement of the syringe 30 closer to the threaded lead screw shaft 54resulting in a smaller syringe drive system 64.

Other plunger flange shapes are possible. For example, a plunger flangehaving a rectangular shape may be used having two guide rail slotsformed on the edge opposite the threaded lead screw engaging portion.Two guide rails positioned on either side of the lead screw may add evenfurther stability to the plunger, especially under heavy loads.

Referring now to FIG. 6, one of the stem arms of the plunger 42, in thiscase the nearmost arm 56, is provided with a linear grid made up of aseries of equally spaced markers 58 along the length of the stem arm.The distal markers 58 at the distal end 60, which in this embodiment isthe end nearer the stopper 44, are small in comparison to the markers 58at the proximal end 61, which in this embodiment is the end nearer theplunger flange 46. As explained in detail below, these markers 58 servein detecting linear motion of the syringe and provide an indication ofthe amount of fluid remaining in the syringe.

Referring again to FIG. 3, another feature of the syringe 30 is that oneedge of the syringe body flange 40 is provided with identificationmarkers 62 which take the form, in this embodiment, of slots. Asexplained below, these identification markers may be used to provide anindication of the type, e. g., size, of syringe being used. Other typesof markers may be used as well as different numbers of them. Forexample, in one embodiment, it was found to be more effective to use aset of three slots for identification of the syringe.

Turning now to the structure of the syringe driver 66, as shown in FIG.2, the syringe 30 fits onto selected parts of the syringe driver 66. Thesyringe driver 66 has a casing 68 upon which a threaded lead screw shaft54 is rotatably mounted. Preferably, the thread on the shaft 54 issquare cut. The shaft 54 is journalled at either end on bearings and isdriven by means of a motor (not shown) mounted alongside but spacedapart from the threaded shaft 54. The motor and threaded shaft 54 areconnected by a series of gears, including a drive gear 70. The motor maybe powered by batteries (not shown) located in the casing 68 or, in thecase of a non-ambulatory syringe driver, by main outlet power.

The syringe body 32 rests on the casing 68 and the flange 46 end of theplunger 42 lies parallel with, but spaced apart from, the threaded shaft54 with the threaded portion 50 directly engaging the threaded shaft 54such that the threaded portion is engaged with and can follow thethreaded shaft. A substantial advantage of the syringe driver system 64embodying the present invention is that, because no stem arm is presentin the plunger flange 42 in the area extending from the threaded portion50 of the plunger flange 46 to the stopper 44, the threaded shaft 54 canbe accommodated in that area so as to take up much less space andeffectively be within the confines of the size of the syringe when fullyextended. This is shown in FIG. 2 although in this figure, the syringeis not fully extended. This is in stark contrast to the arrangementshown in FIG. 1 for the conventional syringe driver where the threadedshaft is located outside the confines of the syringe.

The casing 68 includes an elongate guide rail 72 which extends parallelto the threaded shaft 54. The guide rail 72 engages the guide slot 52formed in the plunger flange 46 (FIG. 3). Thus, the plunger flange 46 issecurely sandwiched between the guide rail 72 and the threaded shaft 54and the threaded portion 50 of the plunger flange 46 is securely seatedon the threaded shaft 54 such that any rotation of the threaded shaft 54causes the plunger flange 46 to follow the rotation and drive theplunger 42 into or out of the syringe body 32 as desired. Additionally,use of the guide system prevents the syringe plunger from rotating. Theuse of a guide rail is particularly advantageous when viscous fluids arein the syringe or a high impedance is encountered downstream whichoppose movement of the plunger into the syringe body. Such oppositionforces can cause the syringe plunger flange to tend to raise up and offthe lead screw thus disengaging. Absent the guide rail holding theplunger flange in contact with the lead screw, infusion of the contentsof the syringe may not occur.

The guide rail 72 provides a guide for the travel of the plunger flange46 and also prevents the threaded portion 50 from being lifted up andaway from the threaded shaft 54 during rotation of the shaft 54. Mostimportantly, because of the direct mechanical engagement between thethreaded shaft 54 and the plunger flange 46, there are no moving partsinvolved between the threaded shaft 54 and the plunger 42 so that thereis direct transfer of motion from the shaft 54 to the plunger 42. Thisarrangement provides a simple and accurate drive system for the syringedriver.

A considerable advantage of this syringe driver arrangement describedabove and shown in the figures is that, as the majority of syringes aredisposable syringes, any syringe used in the syringe driver systemembodying the present invention is not going to be subject to wear dueto prolonged use since the threaded portion of the plunger is onlyengaged with the threaded shaft for one use. Thus, each time the syringedriver 66 is loaded with a new syringe 30, a new threaded shaft engagingportion 50 is provided to give an accurate direct mechanical engagementbetween the plunger 42 and the threaded shaft 54.

The direct engagement of the threaded portion 50 of the plunger flange46 with the threaded shaft 54 has been tested and the results areexceptionally good. Volumetric tests yielded “trumpet” curves with anaccuracy better than 5% at 2 minute intervals at a rate of 5 millilitersper hour.

With continuing reference to FIG. 2, the casing 68 is provided with twoopto-electronic detectors in this embodiment. The first detector 74 isused to provide detection of linear movement of the syringe plunger anda warning when the near-end-of-infusion (NEOI) point is being reached,i. e., when the syringe is almost empty and needs replacement. Thedetector 74 is mounted on the casing 68 adjacent the stem arm 56 uponwhich the markers 58, 60 (FIG. 6) are formed. The detector 74 is ofsubstantially horse-shoe shape, one end of the horse shoe housing alight source and the other end of the horse shoe housing a pair ofdetectors located alongside one another such that light from the lightsource is blocked by the arm 56 so that neither of the detectors areilluminated but, when a marker 58 is positioned between the light sourceand the detectors, one of the detectors is illuminated. As the syringeplunger travels along the shaft 54, equally spaced dark and lightsignals are detected by the optoelectronics switch 74. The timing ofthese signals can be used by a control system to confirm that theplunger is moving at the correct rate. Similarly, a lack of detection ofdark and light signals indicates to the syringe driver that no movementof the syringe plunger is occurring. This may be the result of anexhausted syringe, which means that the end of infusion (“EOI”) has beenreached, thus also providing detection of such condition. The processorof the syringe driver may be programmed to determine the EOI after firstdetecting the NEOI and to provide an audible and/or visual alarm orother indication of the EOI.

Since the markers at the NEOI point, which is at the proximal end 61,are larger than the markers 58 along the rest of the length of the arm,the larger markers allow the light source of the NEOI detector toilluminate both detectors. This serves as an indication to a controlsystem of the syringe driver that there has been a transition from thesmaller markers at the distal end 60 to the larger markers at theproximal end 61 which means that the NEOI point is being approached andthe syringe needs to be replaced. Such detection can trigger an alarm,provide a warning light or other form of indication. Clearly, therespective sizes of the markings can be reversed or the shapes orconfigurations can be changed to obtain the same effect and/or thetransition or approach of the NEOI point can be encoded differently onthe arm.

The second detector 76 is a syringe identification detector which againcomprises a horse-shoe shaped optoelectronic detector having a lightsource in one of its ends and at least a pair of detectors in its otherend. A plurality of such optoelectronic detectors arranged adjacent oneanother can be provided instead of just one. When a syringe 30 isinserted in the casing 68, the identification markers 62 (FIG. 3) arelocated between the respective ends of the optoelectronic detector 76,or detectors, so as to provide an indication of the type of syringeinserted in the casing 68 and any other characteristics that the controlsystem of the syringe driver 66 may need to operate in accordance withthe specific syringe inserted in the syringe driver. The ability of thesyringe driver to automatically recognize a characteristic orcharacteristics of the syringe, for example the volume of a syringeinserted in the driver, means that this information need not be enteredmanually thus lessening the possibility of human error.

Referring now to FIG. 8, a simplified drawing of a casing 68 is shown.The casing 68 comprises a generally elongate and rectangular housingcomprising a base 80 and a cover 82 that is hinged to the base 80. Thecasing 68 is dimensioned to accommodate a fully extended syringe 30,although the syringe shown in FIG. 8 is only partially extended inaccordance with this particular infusion. Inner details of the case,such as the motor, gears, and lead screw, are not shown for purposes ofclarity of illustration of the casing. The motor is controlled by acontrol panel 84 on the cover 82 and the settings and operation of thedriver can be monitored by a display 86 for indicating pump operatingparameters such as the infusion rate. The display 86 is located on thecover 82 adjacent the control panel. A control system (not shown)comprising a control circuit or microprocessor is housed within thecasing 68 and connected to the control panel and display.

The detectors 74, 76 are linked to the control system to provideinformation about the type of syringe inserted in the casing 68 as wellas the progress of the infusion and proximity of the NEOI point. Thecontrol system can be programmed by the control panel 84 to infuse aparticular volume of fluid per unit time or to vary the number ofinfusions of a particular dose required at respective times inaccordance with the drug characteristics and any relevant patientinformation.

The use of the identification markers 62 and the detector 76, ordetectors, enables the syringe driver embodying the present invention torecognize the volume of the syringe installed. Based on thisinformation, the control system can be calibrated in milliliters perhour rather than millimeters per hour. This is an improvement overconventional ambulatory syringe drivers which calibrate only inmillimeters per hour. Thus, medical staff will find syringe driversembodying the present invention easier to use since medical staff arewell-used to dealing in volumes per unit time rather than lengths perunit time.

Two particular embodiments of a casing 68 are now discussed. The firstembodiment is shown in FIGS. 9 and 10. The cover 88 is hinged to thebase 90 along the central axis of the threaded shaft 54. A spring plate92 extends along the base 90 and is provided with a guide rail 72. Whenthe cover 88 is opened, the syringe 30 can be inserted in the cover in acassette-like manner and the threaded portion 50 of the plunger flange46 engaged with the threaded shaft 54. The plunger body 32 rests onanother area of the base 90 of the casing. The cover 88 can then beclosed as shown in FIG. 10. As the cover 88 is pressed down, the springplate 92 is pushed away from the threaded shaft 54 until the cover isfully closed at which point the guide rail 72 on the spring plate 92 issprung into position into the guide slot 52 in the plunger flange 46.When the syringe is correctly inserted the spring plate 92 is locked inplace by the complete closure of the cover 88. In an alternateembodiment (not shown) the spring plate 92 extends upward and the cover88 includes a channel. Upon closure of the cover 88 the top of thespring plate 92 engages the channel. In either embodiment, if thesyringe 30 is inserted incorrectly the cover 88 cannot be closed.

The internal surface contours of the base 90 correspond closely to theshape of the outer periphery of the syringe body flange 40 thus securingthe syringe body 32 within the casing 68 and preventing any turning orre-alignment of the syringe body with respect to the casing. Preferably,a pair of guide ribs (not shown) are molded into the cover 88 to receivea longitudinal edge of the syringe body flange 40 and prevent movementof the syringe body 32 longitudinally with respect to the casing 68.

Referring to FIGS. 11 and 12, in another embodiment of the casing 68,the cover 94 is not hinged about the threaded shaft 54. In thisconfiguration, the guide rail 72 is provided on the lid of the cover 94.The syringe 30 is inserted in the cover 94 and there is enough play wheninserting the syringe 30 in the cover 94 for the edge of the plungerflange 46 to slide over the guide rail 72 until the guide rail 72 isengaged in the guide slot 52. Thus, the threaded portion 50 isdownwardly depending and pointing substantially towards the threadedshaft 54. The cover 94 is hinged on the far side of the casing 68 tobring the threaded portion 50 into direct engagement with the threadedshaft 54 at which point the cover 94 is closed on the base portion 96 asshown in FIG. 12. Thus, the action of loading and closing the casing 68,in both the embodiments shown in FIGS. 9 to 12, locates the threadedportion 50 of the plunger flange 46 into direct engagement with thethreaded shaft 54. The successful closing of the casing 68 is preferablymonitored by an optical switch, microswitch or the like which disablesthe motor and/or any control devices so as to prevent the syringe driverfrom working without a syringe being properly loaded.

In one embodiment, conveniently, different volumes of syringes all havecommon exterior characteristics allowing all volumes of syringes to becorrectly loaded in the same syringe driver. The volume of the syringecan then be determined by using the coded identification markers 62which are molded into the syringe body flange 40 of the syringe body 32.

Although the syringe disclosed in the above embodiments has beenprovided with additional features, the syringe can still function as anormal syringe for use without the syringe driver. Conveniently, thesyringes for use with the syringe driver are sold as dedicated units forloading in the syringe driver and may come in the form of pre-filledsyringes. Preferably, the syringes 30 used with the syringe driverembodying the present invention have a higher width to length ratio thannormal syringes so that the length of the syringe is minimized for agiven volume of syringe. It is envisaged that the use of non-cylindricalsyringe bodies could be advantageous as a means of registering thesyringe body 32 in the casing 68 or to provide a more convenient caseshape to the user.

While the above-mentioned examples describe a syringe driver for asingle syringe, a syringe driver using the same concepts can be providedfor driving multiple syringes. The above-mentioned examples of theplunger involve the use of a threaded portion 50 on the plunger flange46 for engaging the threaded lead screw shaft 54. The invention,however, can still be implemented by engaging an unmodified edge of aplunger flange 46 directly with the threaded shaft 54, the edge of theplunger flange sitting between the threads of the threaded shaft 54. Itis envisaged that the arrangement of the guide slot 52 and guide rail 72can be reversed or otherwise implemented. For example, the guide rail 72can be replaced with an elongate channel running substantially parallelto the threaded shaft 54 and the guide slot 52 replaced by a projectionextending from the plunger for reception in the channel. Alternatively,an elongate plunger stem arm may be formed on the plunger at a positionsubstantially opposite the position at which the plunger is engaged withthe threaded shaft and a guiding system comprising the arm and abifurcated element are located on the casing 68 to straddle the arm.

The syringe driver can also be provided with means to sense that asyringe has been removed from the casing or the casing is empty. Suchsensing means can comprise an optical detector, microswitch or the like.The sensing means can provide a signal to a stop valve or the like toclose the fluid line to a patient to prevent syphoning of the medicamentin the line when the syringe has been removed from the casing or if thecasing is empty.

Referring now to FIG. 13, a schematic, block diagram of an example of acompact syringe drive system incorporating aspects of the invention ispresented. Additionally, the compact syringe drive system of FIG. 13includes aspects of FIGS. 9 and 10. In this layout, the syringe body 32is located adjacent the battery 100. At the opposite end, the motor 102is connected to a gear drive 70 which drives the lead screw 54. Theinternal components of the gear drive 70 are not shown in the interestof retaining clarity in the drawing. A motor encoder disk 104 for use indetecting the speed and direction of the motor is provided. An opticalswitch (not shown) is mounted so as to read the encoder disk 104. Apartial view of a bearing block 103 supporting one end of the lead screw54 is shown. This arrangement results in a compact syringe drive system.

Although the system for detecting the near-end-of-infusion was shown anddescribed above as a series of markers formed into a stem arm, otherapproaches may be possible. One approach that may be used is that shownin U.S. Pat. No. 5,236,416 to McDaniel et al. where a stationarydetector is used in conjunction with a marker. The marker moves with thesyringe plunger and interacts with the stationary detector, which maytake the form of a potentiometer. In the present case, a marker, such asspur, could be molded or otherwise formed onto the plunger flange 46 orother movable part associated with the plunger. A potentiometerfunctioning as the detector could be located in the pump case in aposition such that the spur of the plunger flange 46 would contact thepotentiometer during its entire range of travel. The output of thepotentiometer could then be used to monitor the position of the plungerflange 46 and thus the plunger so that the near-end-of-infusion pointcould be determined.

Thus the syringe driver of the present invention has fewer parts in thata driver block is not used with the resulting decrease in expense andincrease in manufacturing ease. Additionally, the system is more compactand the need for maintenance should be lowered because of this lack of adriver block which is prone to wear.

It will be apparent from the foregoing that while particular forms ofthe invention have been illustrated and described, various modificationscan be made without departing from the spirit and scope of theinvention. Accordingly, it is not intended that the invention belimited, except as by the appended claims.

What is claimed is:
 1. A syringe driver system for expelling fluid froma syringe body, the system comprising: a syringe body having a distalend, a proximal end, and a side wall, the syringe body formed with anozzle end at the distal end; a rotatable threaded shaft; and a plungerhaving a stopper and a plunger flange interconnected by a plunger stem,the plunger flange extending radially outwardly from the plunger stemand adapted to directly engage the threaded shaft such that rotation ofthe shaft drives the plunger into the syringe body.
 2. The syringedriver system of claim 1 wherein the plunger is formed with a shaftengaging portion to engage with and follow the threaded shaft.
 3. Thesyringe driver system of claim 2 wherein the shaft engaging portioncomprises a threaded portion formed in the plunger.
 4. The syringedriver system of claim 3 wherein the threaded portion is molded into theplunger.
 5. The syringe driver system of claim 2 wherein the shaftengaging portion comprises at least one recessed half-nut.
 6. Thesyringe driver system of claim 2 wherein the flange comprises at leastone disk, the shaft engaging portion comprising part of the flange. 7.The syringe driver system of claim 6 wherein the edges of the flangeadjacent the shaft engaging portion are formed to guide the shaftengaging portion onto the threaded shaft.
 8. The syringe driver systemof claim 1 further comprising a guide system to secure the plunger indirect engagement with the threaded shaft.
 9. The syringe driver systemof claim 8 wherein the guide system comprises a first guiding elementrunning substantially parallel to the threaded shaft and a secondguiding element carried by the plunger at a position substantiallyopposite the position at which the plunger engages the threaded shaftsuch that the first and second guiding elements engage.
 10. The syringeof claim 9 wherein the first guiding element comprises a guide rail andthe second guiding element comprises a slot.
 11. The syringe of claim 9wherein the first guiding element comprises a channel and the secondguiding element comprises a projection.
 12. The syringe driver system ofclaim 8 wherein the plunger comprises an elongate arm positionedsubstantially opposite the position at which the plunger is engaged withthe threaded shaft and the first guiding element comprises the arm andthe second guiding element comprises a bifurcated element for straddlingthe arm.
 13. The syringe driver system of claim 1 wherein the plungercomprises a plurality of markings adapted to indicate the movement andposition of the plunger within the syringe body.
 14. The syringe driversystem of claim 13 wherein the plurality of markings comprise a lineargrid.
 15. The syringe driver system of claim 13 wherein an area of theplunger between the markers is substantially opaque and the markingscomprise substantially transparent portions.
 16. The syringe driversystem of claim 13 further comprising a detection system having a lightsource and a plurality of detectors, the detection system positionedadjacent a portion of the plunger on which the markings are located suchthat the light source is on one side of the portion of the plunger andthe plurality of detectors is on the opposite side of the portion of theplunger and wherein the markings on the portion of the plunger at a nearend of infusion (NEOI) point of the syringe have a first size and themarkings elsewhere on the portion of the plunger have a second sizedifferent than the first size such that the markings at the NEOI pointallow illumination of a first number of the detectors and the markingselsewhere allow illumination of a second number of detectors differentthan the first number of detectors.
 17. The system of claim 1 whereinthe plunger includes a marker indicative of the position of the plunger;and the system further comprising a detector positioned so as tointeract with the marker and provide a signal indicative of the positionof the marker.
 18. The system of claim 17 wherein the marker comprises aspur formed on the plunger and the detector comprises a potentiometer.19. The system of claim 1 wherein the syringe includes a syringeidentification marking indicative of a characteristic of the syringe;and the system further comprising a syringe detection system including adetector for detecting the identification marking of the syringe, thesyringe detector system adapted to provide a signal in accordance withthe identification marking detected.
 20. The syringe driver system ofclaim 1 wherein the outwardly extending plunger flange includes an outerflange edge that directly engages the threads of the threaded shaft suchthat rotation of the threaded shaft drives the plunger into the/syringebody.
 21. A syringe driver system for expelling fluid from a syringebody, the syringe driver comprising: a rotatable threaded shaft; aplunger adapted to directly engage the threaded shaft such that rotationof the shaft drives the plunger into the syringe body; a guide system tosecure the plunger in direct engagement with the threaded shaft, theguide system comprising a first guiding element running substantiallyparallel to the threaded shaft and a second guiding element carried bythe plunger at a position substantially opposite the position at whichthe plunger engages the threaded shaft such that the first and secondguiding elements engage; wherein the plunger comprises an elongate armpositioned substantially opposite the position at which the plunger isengaged with the threaded shaft and the first guiding element comprisesthe arm and the second guiding element comprises a bifurcated elementfor straddling the arm.
 22. A syringe driver system for expelling fluidfrom a syringe body, the syringe driver comprising: a rotatable threadedshaft; and a plunger adapted to directly engage the threaded shaft suchthat rotation of the shaft drives the plunger into the syringe body, theplunger comprising a plurality of markings adapted to indicate themovement and position of the plunger within the syringe body; and adetection system having a light source and a plurality of detectors, thedetection system positioned adjacent a portion of the plunger on whichthe markings are located such that the light source is on one side ofthe portion of the plunger and the plurality of detectors is on theopposite side of the portion of the plunger; wherein the markings on theportion of the plunger at a near end of infusion (NEOI) point of thesyringe have a first size and the markings elsewhere on the portion ofthe plunger have a second size different than the first size such thatthe markings at the NEOI point allow illumination of a first number ofthe detectors and the markings elsewhere allow illumination of a secondnumber of detectors different than the first number of detectors.
 23. Asyringe driver system for expelling fluid from a syringe body, thesystem comprising: a syringe body having a distal end, a proximal end,and a side wall, the syringe body formed with a nozzle end at the distalend; a rotatable threaded shaft; and a plunger having a stopper and aplunger flange interconnected by a plunger stem, the plunger flangeextending radially outwardly from the plunger stem and adapted todirectly engage the threaded shaft such that rotation of the shaftdrives the plunger into the syringe body, the plunger comprising aplurality of markings adapted to indicate the movement and position ofthe plunger within the syringe body.
 24. The syringe driver system ofclaim 23 wherein the plurality of markings comprise a linear grid. 25.The syringe driver system of claim 23 wherein an area of the plungerbetween the markers is substantially opaque and the markings comprisesubstantially transparent portions.
 26. The syringe driver system ofclaim 23 further comprising a detection system having a light source anda plurality of detectors, the detection system positioned adjacent aportion of the plunger on which the markings are located such that thelight source is on one side of the portion of the plunger and theplurality of detectors is on the opposite side of the portion of theplunger and wherein the markings on the portion of the plunger at a nearend of infusion (NEOI) point of the syringe have a first size and themarkings elsewhere on the portion of the plunger have a second sizedifferent than the first size such that the markings at the NEOI pointallow illumination of a first number of the detectors and the markingselsewhere allow illumination of a second number of detectors differentthan the first number of detectors.
 27. A syringe driver system forexpelling fluid from a syringe body, the system comprising: a syringebody having a distal end, a proximal end, and a side wall, the syringebody formed with a nozzle end at the distal end; a rotatable threadedshaft; and a plunger having a stopper and a plunger flangeinterconnected by a plunger stem, the plunger flange extending radiallyoutwardly from the plunger stem and adapted to directly engage thethreaded shaft such that rotation of the shaft drives the plunger intothe syringe body, the plunger including a marker indicative of theposition of the plunger; and a detector positioned so as to interactwith the marker and provide a signal indicative of the position of themarker.
 28. The system of claim 27 wherein the marker comprises a spurformed on the plunger and the detector comprises a potentiometer.
 29. Asyringe driver system for expelling fluid from a syringe having asyringe body, the syringe having a syringe identification markingindicative of a characteristic of the syringe, the system comprising: asyringe body having a distal end, a proximal end, and a side wall, thesyringe body formed with a nozzle end at the distal end; a rotatablethreaded shaft; a plunger having a stopper and a plunger flangeinterconnected by a plunger stem, the plunger flange extending radiallyoutwardly from the plunger stem and adapted to directly engage thethreaded shaft such that rotation of the shaft drives the plunger intothe syringe body; and a syringe detection system including a detectorfor detecting the identification marking of the syringe, the syringedetection system adapted to provide a signal in accordance with theidentification marking detected.